This invention relates to a muffling and denitrating apparatus for reducing exhaust sound generated by a combustion engine and concurrently reducing a concentration of nitrogen oxides contained in exhaust gas of the engine. Also, the present invention relates to a muffling and denitrating apparatus equipped with a dust collecting mechanism for removing particulates from the exhaust gas. Further, the present invention relates to modified carbon fibers or carbon particles used for the muffling and denitrating apparatus and a process for producing the same.
In various kinds of combustion engines including, particularly, a moving combustion engine such as an automobile or the like, sound-damping or a decrease in noise attendant upon generation and discharge of exhaust gas from the combustion engine and denitration or a decrease in concentration of nitrogen oxides (NO.sub.x) in the exhaust gas are highly desirable.
A conventional muffler for an automobile is provided therein with a plurality of rectifying plates for sound-damping. Unfortunately, such arrangement of the rectifying plates causes a back pressure to be increased, resulting in combustion efficiency of an automobile being substantially decreased, so that fuel consumption efficiency is deteriorated.
One of denitrating devices which have been conventionally known in the art uses a noble metal catalyst made of noble metal such as platinum or the like. Unfortunately, platinum is highly expensive and readily poisoned by impurities contained in exhaust gas of a combustion engine, resulting in catalytic performance of the catalyst being deteriorated. In particular, this leads to a failure in application of the catalyst to a diesel engine. Also, there is known denitration using carbon fibers, as taught in Proceedings of the 69th National Convention Lecture of Japan Society of Mechanical Engineers, "1508 Research of Denitrating Apparatus by New Material", pp 450-452. However, the denitration still requires improvements such as an improvement in denitrating performance of the material, an improvement in the denitrating apparatus, and the like.
A conventional engine for an automobile generally employs a denitrating device using a catalyst which is rendered active at an elevated temperature. The denitrating device is installed at a high temperature site in proximity to an outlet of the engine. Also, the engine is provided with a muffling device, which is located at a position of a reduced temperature on a downstream side in a direction of flow of exhaust gas based on the denitrating device. Thus, the muffling device and denitrating device are arranged separate from each other, to thereby cause complication of an exhaust system of the automobile and an increase in manufacturing cost of the exhaust system.
In addition, it is known that particulates, such as soot, contained in exhaust gas of a combustion engine causes air pollution, therefore, removal of the particulates as well as the above-described sound-damping and denitration is highly desired.